Welding current indicator and lockout



May 10, 1949. E. M. CALLENDER ETAL 2,470,067

WELDING CURRENT INDICATOR AND LOCK-OUT 2 Sheets-Sheet 1 Filed Feb. 24, 1944 INVENTORS.

Edw'mMCaHenden Qoberc S. Dha'u BY Herbert DVanSciver- JONErZOU 625d; 9585 May 10, 1949. E. M. CALLENDER ETAL WELDING CURRENT INDICATOR AND LOCK-OUT Filed Feb. 24, 1944 2 Sheets-Sheet )2 5; 99 9s 21 i350 Ia I mi 2 1 B3 131/ 152 {LS-L Tnocor.

JNVENTORS *Edw'mMCallender +1 lobtegkvi hqir. BY er er anSciver.

ATT

Patented May 10, 1949 2,470,067

UNITED STATES PATENT OFFICE WELDING CURRENT INDICATOR AND LOCKOUT Edwin M. Callender, Cynwyd, Robert S. Phair, Philadelphia, and Herbert D. Van Sciver, Merion, Pa., assignors to The Budd Company, Philadelphia, Pa., a corporation of Pennsylvama Application February 24, 1944, Serial No. 523,692

Claims. (Cl. 177311) This invention relates to an electrical system for indicating limits in current flow. More particularly the invention relates to apparatus and circuits for visually or audibly indicating our- ,main alternating current power source is in- 2 dicated by the mains In and l I with the primary 12 of the welding transformer 3 connected in series. The secondary M of the welding transformer has connection to the roller rent limits or effecting disconnection of the con- 5 electrodes [5 and I6, which are shown placed trolled circuit at such limits. The invention is in juxtaposition with reference to the workpiece useful in any operating circuit but has particu- I1. lar utility in connection with seam welding where Also in series with the primary I2 of the weldpower is applied with substantial continuity, ing transformer l3 are ignitrons l8 and 19 conthere being a series of weld applications as dis- 10 nected in inverse parallel, each having anodes tinguished from the single application of spot 20, pool cathodes 2| and igniter elements 22. By welding. the term inversely connected is meant the In spot resistance welding means have been usual connection of one side of the power source .devised which effectively control the approxn and the welding transformer primary to the mate heat at the weld. This is of considerable cathode of one tube and the anode of the other practical importance as afiording a gauge or so that advantage may be taken of both posistandard for' determining the soundness of the tive and negative half cy o e u ce 011 weld and consequently the strength of the welded r nt. The timer control is one of the convenstructure. However, the means applicable to spot tional fOImS and is Shown as connected to the welding are not, in general, satisfactory for seam ode 0 Of t e ighitrons, the igniters a d welding. There are several reasons for this, ina direct current power source 23. The timer with cluding the difference in the mode of current its accessory circuits functions to control the application and the difficulty of providing a high time of weld current flow, the time between welds frequency indicating meter which will not burn and the amount of energy pe Weld. out on overload or be damaged by needle swing. 25 T c ntr l ir B i related to the p m y Objects of the present invention include the irc it f th p w r our m in lilli and provision of means for indicating the limits of includes a current transformer having a p current for said seam welding, for providing inmary 3| of a single conductor section, and a dicating circuits which may be utilized for visual closely coupled on ry 32 Surrounding the or audible indicators; for providing indicating 30 p m mh v e pl r i y f p 33 f fymeans of substantial ruggedness for continuous the transformer These p a 0 current operation; for providing automatic lockecte to Switches 3 and through a esi t 35 out apparatus for seam weld and similar circuits; and a Potential divider 36 t0 the g ound it and for providing lock-out means for. main circuit the 011ter end of the Secondary Additional current variation which operates Within a satis- 35 v r hunt resi or 38, nd a h rt circuiting factory range of sensitivity; and for providin Shunt 39 to prevent excessive voltages on disuse current lock-out means adjustable to any degree of the indicator Circuit, are also providedof percentage variation of current Included also in the COl'ltl'Ol circuit B isarectifier The objects of the invention are effectuated by 40 connected at its input p t t the grounded the circuit and circuit apparatus hereinafter de- 40 end of the current transformer and to the movscribed and shown in the accompanyin drawable arm 4| Of the potential divider 36. The ings, in i rectifier provides rectified current through a Figure 11 View Shgwing a diagram f the variable resistor 42 to the capacitor bank 43 inindicating circuit; and cluding capacitors 44, 45, 46 the latter having Figure 2 is View showing the accessory 10ck selective switch connections to the resistor side o t i cuit, of the rectified circuit whereby the uni-direc- Referring to Figure 1, the circuit is di d d tional and on-off undulations of the rectified curt sections C and D, A indicating the rent may be controlled at will. A volt meter Welding circ it, 13 the in i t 3 th ind t 4! is connected in shunt with the capacitor bank reference circuit, and D the initiating and in- 43, this meter being highly damped d Sensitive dicator operating circuit. for low voltages. The capacitor bank 43 assists The welding circuit A is diagrammatic of the in providing stable needle indications in this conventional electronically controlled resistance meter and fairly uniform Voltage 011 the put welding circuit as utilized in seam welding. The terminals 50 and 5| of this branch circuit. A

resistor 48 in series with a potential divider 49 cuit C as shown in connection with the control 1 circuit. This circuit includes an alternating current transformer 60 having a primary 6i connected to source mains B2 and secondaries 63', 64, 65 and 66. secondaries '6'4 and 65 form constituent parts of a rectifying circuit, the terminals of secondary 64 connecting to the anodes Bi, and the terminals of secondary 6'5 having connection to the filament 68 of the rectifying tube 69. The mid-point 10 er the secondary 6:! forms one side of the rectified circuit and constitutes the zero line having connection with the point 56 in the control circuit. A filter, including the choke I l, capacitor 12, and resistor 73, cooperates in producing a direct current voltage between the zero line 14 and the direct current potential line 15. In order to establish a constant potential between these lines of potential differences, a glow tube 16 is connected between them as shown. The load of this rectified constant potential circuit includes the two potential dividers "H and 18 connected in parallel, the resistor 1-9 and the vacuum tube '80 together-with the bias resistor 5-! and bias capacitor -82. The tube it is triode, the anode 83 ofwhich is-connected to the resistor 19, the indirectly heated cathode 8& being connected to the bias resistor 8L The heating filament 85 of tube 80, is connected to the secondary E6 of transformer 60 and the grid 86 is connected to a branch circuit leading from the reference line '14 througha capaci-tor -81 and resistor 88 to the, movable "arm 5;] of the potential divider 59 in the control-circuit. The connection of the grid is at a pointintermediate the resistor 88 and capacitor 81. The point 50 on the other side of the resistor 48 is connected directly to the zero line #4 of the reference circuit -C.

It thus appears thatby means of the circuit described to this point "a, constant-potentialdirect current may be passed through the tube 86, the

value of the current through the tube and consequently through the potential dividers "H and 18 varying directly inaccordance with the variation of the potential of grid "86 which in turn varies directly with the variation in potential across the resistor 48 and potential divider 49 or other operation and rnay e1 bin'ghormally deenergized and its switch open during the'normal operating range. rhe'reiayso ondiminution of currenttothe lower l'iihitcloses its switch which is effe cfiilfe to indicate 'bynieans'or Visual 'or audible sierialsth'e lqvfr liinito'f currentvaria- 'tion. si'nulanyreiay 9|, when the upper limit 'tim i'ng "circuits and the welding transfor er in the 'ciiflhtfilellisfdffilel '30. "la-predetermined l of current flow is reached, functions to close its switch and indicate the upper limit of current flow. As shown, a circuit may be established from the alternating current source, and through the initiating switch 96 and a timer relay coil 91, the latter serving to close contacts [2 5, I26 in circuits I21, I28 to begin the timing cycle in the timing control mechanism not herein shown. When this "circuit also is closed current passes through normally closed switch contacts 92 and 9.3, the lamp 923 and the bell 99, the latter operating only on the beginning or ending of current flow. 'It is pointedout that the circuit from source point 95. is through the lamp and bell to closed relay contact 92', the circuit from 93 being through the shunt conductor I00 and initiating switch Qlift'o source point 94. Contact point 92 of relay 90 is connected also to contact I01, point HH and the companion contact I02 forming points of engagement with the armature of relay 9! which is normally open during operation of the main circuit. It is observed that when the contacts of relay "9b are open and "the contacts of relay 91 are closed the bell and lamp, circuit passes through the contacts of relay '91, to c'o'fim plete the, operating circuit '94 9'5. A

In order to operate the relays 8'0 and '91. "at the limit points of current now i "the main circuit electronic means, are provided which are effective to pass current at these limits. Accordingly the operating circuit includes two g'asfilled tetrodes or thy-ratrons. 104 and 105, one being in series with each relay and each relay thyra-tron branch circuit 'forlh'ih'g parallel branches across an "alterha'ting current source through transformer "16. -Thy ra'tifon 1'04 includes the usual anode 101, screen grid 1'08, control grid I09 and indirectly 'h'eated cathode fill, the filament 111 having c' ri'nebtibn to the secondary 63 of transformer 80. for its heatin Current. The anode T01 is connectedto one end or the relay 91 the other mdhavirrg crsnnecndnfto the point 1T2 at the trlii'sfiiii nier I106. screen .grid W8- has connection to the fathod e 'ahdtlie control grid "[9 is connected by conductor H3 to the contact arm, [4 of the potential "divider 18. Also 'thyr'a'troh 1115. has an anode l l'5,"scieefn screen grid H S, control grid n, cathode, 11;8 and filament 1T9, "the amerit being connected disc to secondary "ts "or nansfcsrmer to, screen grid H6 being "cannecrea't ftheeamou andftne control grid TI! to "the "inljvabjle arth "of the potential divider 'l"l,ja'nd anode 11?; "having connectiohthiough relay 910 to transformer point H2. The cathodes "of both thyiatlon's ar -crinhected enemy to the 'eeticurrenrpdtentin line or the operatin brain circuit and {brim-contr l grids are c'on'nec'tedf'to the "same line through repeaters I2 I; ana "[12,.

the other accessory equi ment including the cooling apparatus is functioning properly 'for 'the welding spars-nan. Also *the "coil "or reray so is energized "to open its contacts $2, '93. The initiating switch as is then closed jther'eby "causm current "to now throug thetirner relay 91 thus bringing about. "closure or jfli'i'scel'laneoiis m naret "or "the nearomc rrefnt thereupen news *in 3 and simultaneously welding control. 7

. voltage is then "applied across the rectifier 40 and made effective across the resistor 48 thus producing at the resistor a voltage variable directly in accordance with variation in current flow. Because of the capacitor bank 43 the voltage value imposed on the grid 86 of tube 80 approximates a constant percentage of the average value of the on-off load current. This voltage variation is imposed upon the grid 86 of tube 80 in the load circuit of the constant potential reference circuit C so that in the potential dividers H and "I8 of this load circuit, variation of the variable =-current of control resistor 46 is imposed upon the reference circuit.

'18 conductors lead to control grids in the thyra- From these resistors 11 and trons I04 and I05, I04 being normally non-conducting during the welding operation but becoming conductive on excess current flow when the current reaches and exceeds the upper limits of its normal current range in the welding circuit. Thyratron I05, however, is normally conductive prior to initiation of the welding cycle and also during the cycle is conductive within the normal range of the average welding current flow. Should, however, the current in the welding circuit diminish and fall below the lower limit of its normal range, the control grid I H, activated from the resistor 11 of the reference circuit, functions to stop the flow of current in the thyratron circuit thereby deenergizing the relay 90 and permitting the contacts 92 and 93 to close. There will result accordingly a visual .signal in the lamp 98 and an audible signal in the bell 99 to indicate that the current flow of the welding circuit is below the normal range and, consequently, the equipment requires adjustment for the securing of proper welds.

While only indicators, such as a lamp or bell, have been referred to as employed for signaling the operator that the welding current is either too strong or too weak, it is obvious that the signaling circuit may be led through a recording instrument which will give a permanent record of the variation of current in the weld circuit. It should also be understood that relays 90 and 9| may be used to cause lock out of the seam, welding or other circuits as illustrated in Fig. 2, thus constituting also an indication of current limits in the load circuit. In this figure is shown a modified D circuit section Da. which may be substituted for the D section of Fig. 1 with external connection at 94, 95 as in the D section and similar connections to contacts 92, 93 of relay 90 and contacts IOI, I02 of relay 9|.

In accordance with this modified circuit, the relay coil I30 is substituted for relay 9! of Fig. 1 and placed in parallel with the lamp and bell 98, 99. Relay I30 functions when energized at the current limits to open the weld roller motor circuit contacts I3I, I32 and, also, to open the contacts I33, I34 in the circuit of relay I35, whereupon contacts I25, I26 of the timer circuit I21, I28 are opened, thereby causing the welding circuit to open. A time delay relay device, shown in Fig. 2 as a square box, is connected between lines 94, 95 to keep current from the idle-closed contacts 92, 93 until relay 90 is energized to open them.

It is pointed out that the voltage meter 41, as used in the control circuit, provides means for indicating the voltage of the rectified current and as such it may be used independently of the circuits C and D. This provides a simple control which is not subject to burning out on slight overload as in the case of thermo-couple meters. This permits adjustment of the resistances so that the appropriate values may be eifective on the reference circuit. These adjustments are provided primarily by the resistors 38, 35, 36 and 42, as well as the capacitors 44, 45 and 46. The various taps 33 on the current transformer 30 are also useful for bringing the apparatus into proper adjustment with the working range of current in the welding circuit.

It is pointed out that while the control is broadly responsive to current, time also is involved due to variation of time constants with current magnitude from on to off position, and, hence, the control may be stated to be a function of the product of current and time.

This is true because of the time lag of the capacitor bank 43 and since resistances are c0- ordinated in both on and off positions so that in these positions time, as well as current magnitude, are interpreted by the meter.

In order that the invention may be set forth with greater clarity, it has been described in connection with a resistance seam welding circuit. However, since the apparatus functions on limit changes in current flow, it is apparent that the same may be usefully applied to other types of working circuits. Modifications, other than as indicated, may be made and, hence, the invention should be interpreted only in connection with the claims as hereto appended.

What is claimed is:

l. A weld current indicator circuit comprising a welding circuit, a control circuit operable on energization to initiate supply of variable welding current in recurrent intervals to said welding circuit, and means responsive to the magnitude of average current in the welding circuit over a time period including said recurrent intervals for indicating an average current limit of a predetermined welding circuit range, said means comprising a constant potential branch circuit, including a vacuum triode, a current transformer connected to said welding circuit, a resistor, a rectified current branch dircuit connected across said transformer and resistor, a capacitor connected across said resistor, connections from the cathode and grid of said tube to opposite ends of said resistor, and means connected to the anode of said tube for indicating a limit of current change in said welding range.

2. A current limit indicator comprising a main circuit, a control circuit operable on energization to initiate supply of variable current in recurrent intervals to said main circuit, a transformer connected to said main circuit, a resistor, a rectified current branch circuit connected across said transformer and resistor, a capacitor connected across said resistor, a constant potential cicuit including a load tube having an anode, cathode and control grid, connections from the cathode and grid of said tube to opposite ends of said resistor, and means connected to the anode of said tube, and dependent on variation of current through said resistor, for indicating a limit of current change in said main circuit over a time period including said recurrent intervals.

3. A current limit indicator comprising a main circuit, a control circuit operable on energization to initiate supply of variable current in recurrent intervals to said main circuit, a transformer connected to said main circuit, a resistor, a rectified current branch circuit connected across said transformer and resistor, a capacitor connected across said resistor, a constant potential circuit 

